Computer Virus takes out towns payroll computer

In light of some recent virus attacks another one has come out which has left a small village without a computer to do all the funding and payrolls. The tow, DALZELL which is a part of Bureau county suffered from a virus that totalled the computer leaving in a un-usable state. Now the point i want to get to is, what the hell is a virus doing on this computer, why if its so critical is it allowed to connect to a network that would allow this to happen or has some one done it with bad intentions? Either way Governments of all kinds and companies to need to rethink what they do on work computers, the sites they visit and the protection they have installed, not that any of this will actually stop a virus but it is always good safe measures to take when working with "critical" information